In an electrical communication system, it is sometimes advantageous to transmit information signals (video, audio, data) over a pair of wires (hereinafter “wire-pair” or “differential pair”) rather than a single wire, wherein the transmitted signal comprises the voltage difference between the wires without regard to the absolute voltages present. Each wire in a wire-pair is susceptible to picking up electrical noise from sources such as lightning, automobile spark plugs, and radio stations, to name but a few. Because this type of noise is common to both wires within a pair, the differential signal is typically not disturbed. This is a fundamental reason for having closely spaced differential pairs.
Of greater concern, however, is the electrical noise that is picked up from nearby wires or pairs of wires that may extend in the same general direction for some distances and not cancel differentially on the victim pair. This is referred to as crosstalk. Particularly, in a communication system involving networked computers, channels are formed by cascading plugs, jacks and cable segments. In such channels, a modular plug often mates with a modular jack, and the proximities and routings of the electrical wires (conductors) and contacting structures within the jack and/or plug also can produce capacitive as well as inductive couplings that generate near-end crosstalk (NEXT) (i.e., the crosstalk measured at an input location corresponding to a source at the same location) as well as far-end crosstalk (FEXT) (i.e., the crosstalk measured at the output location corresponding to a source at the input location). Such crosstalks occur from closely-positioned wires over a short distance.
In all of the above situations, undesirable signals are present on the electrical conductors that can interfere with the information signal. When the same noise signal is added to each wire in the wire-pair, the voltage difference between the wires will remain about the same and “differential” cross-talk is not induced, while at the same time the average voltage on the two wires with respect to ground reference is elevated and “common mode” crosstalk is induced. On the other hand, when an opposite but equal noise signal is added to each wire in the wire pair, the voltage difference between the wires will be elevated and differential crosstalk is induced, while the average voltage on the two wires with respect to ground reference is not elevated and common mode crosstalk is not induced.
U.S. Pat. No. 5,997,358 to Adriaenssens et al. (hereinafter “the '358 patent”) describes a two-stage scheme for compensating differential to differential NEXT for a plug-jack combination (the entire contents of the '358 patent are hereby incorporated herein by reference, as are U.S. Pat. Nos. 5,915,989; 6,042,427; 6,050,843; and 6,270,381). Connectors described in the '358 patent can reduce the internal NEXT (original crosstalk) between the electrical wire pairs of a modular plug by adding a fabricated or artificial crosstalk, usually in the jack, at one or more stages, thereby canceling or reducing the overall crosstalk for the plug-jack combination. The fabricated crosstalk is referred to herein as a compensation crosstalk. This idea can often be implemented by twice crossing the path of one of the differential pairs within the connector relative to the path of another differential pair within the connector, thereby providing two stages of NEXT compensation. Another common technique is to cross the conductors of pairs 1, 2 and 4 (as defined by 47 C.F.R. 68.502), leaving the conductors of pair 3 uncrossed (see, e.g., U.S. Pat. No. 6,464,541 to Hashim et al.), then to include a second compensation stage (e.g., in the form of capacitive compensation using one or more capacitors) on an attached printed wiring board. This scheme can be more efficient at reducing the NEXT than a scheme in which the compensation is added at a single stage, especially when the second and subsequent stages of compensation include a time delay that is selected to account for differences in phase between the offending and compensating crosstalk. This type of arrangement can include capacitive and/or inductive elements that introduce multi-stage crosstalk compensation, and is typically employed in jack lead frames and PWB structures within jacks. These configurations can allow connectors to meet “Category 6” performance standards set forth in ANSI/EIA/TIA 568, which are primary component standards for mated plugs and jacks for transmission frequencies up to 250 MHz.
Alien NEXT is the differential crosstalk that occurs between communication channels. Obviously, physical separation between jacks will help and/or typical crosstalk approaches may be employed. However, a problem case may be “pair 3” of one channel crosstalking to “pair 3” of another channel, even if the pair 3 plug and jack wires in each channel are remote from each other and the only coupling occurs between the routed cabling. This form of alien NEXT occurs because of pair to pair unbalances that exist in the plug-jack combination, which results in mode conversions from differential NEXT to common mode NEXT and vice versa. To reduce this form of alien NEXT, shielded systems containing shielded twisted pairs or foiled twisted pair configurations may be used. However, the inclusion of shields can increase cost of the system. Another approach to reduce or minimize alien NEXT utilizes spatial separation of cables within a channel and/or spatial separation between the jacks in a channel. However, this is typically impractical because bundling of cables and patch cords is common practice due to “real estate” constraints and ease of wire management.
In spite of recent strides made in improving mated connector (i.e., plug-jack) performance, and in particular reducing crosstalk at elevated frequencies (e.g., 500 MHz—see U.S. patent application Ser. No. 10/845,104, entitled NEXT High Frequency Improvement by Using Frequency Dependent Effective Capacitance, filed May 4, 2004, the disclosure of which is hereby incorporated herein by reference), channels utilizing connectors that rely on either these teachings or those of the '358 patent can still exhibit unacceptably high alien NEXT at very high frequencies (e.g., 500 MHz). As such, it would be desirable to provide connectors and channels used thereby with reduced alien NEXT at very high frequencies.
One specific type of communications jack is illustrated in U.S. Pat. No. 6,443,777 to McCurdy, the disclosure of which is hereby incorporated herein in its entirety, and is shown in FIGS. 1 through 2B. In this jack, which is designated broadly at 10, contact wires 12 that serve as signal conductors are mounted to the rear of the jack 10 in cantilever fashion and extend into a window 18 formed in the front wall 16 of the housing 14 of the jack 10 that is sized to receive a mating plug. The contact wires 12 are mounted on a printed wiring board (PWB) 44, which has conductive traces to carry signals to terminals mounted on the jack 10. A cover 22 holds the contact wires 12 in place. As can be seen in FIGS. 1A and 2, the contact wires 12 of the jack 10 have free end sections 19 that are generally parallel to each other. In front of the locations 20 on the contact wires 12 that the blades of a mating plug contact, no current flows, so only capacitive coupling (and accompanying crosstalk) occurs between individual lead frames 12 at these locations. Rearward of this contact point, in which current flows, both inductive and capacitive coupling/crosstalk occur.
The cross-section of the contact wires 12 at the contact point is shown in FIG. 2A. Pair to pair calculated crosstalk values for this section of the jack are set forth below in Table 1.
TABLE 1NEAR END CROSSTALK RESULTS - INLINE STRUCTUREPair A to BPair A to BPair B to ADIFF TO DIFF NEXTDIFF TO COM NEXTDIFF TO COM NEXTPair A to BXLXCTOTALXLXCTOTALXLXCTOTAL1 to 3−21.65−3.76−25.010000003 to 2−7.38−1.27−8.6517.783.5121.29−7.13−1.87−9.001 to 21.850.552.40−5.38−0.88−6.26−5.38−0.88−6.26units for all values in mV/V/in.In Table 1, as well in subsequent tables to be presented, all tabulated inductive responses (XL) were derived using calculations that assumed magnetic coupling between line filaments, and tabulated capacitive responses (XC) used calculations based on capacitive coupling between circular wires having circumference equivalent to actual 10×17 mil cross-sections. (Equation references are in Walker, Capacitance, Inductance, and Crosstalk Analysis, Sections 2.2.8 and 2.3.8). The latter calculations are also approximate because shielding effects are not taken into consideration, but the results are sufficient for demonstrating significant contrasts. Further, differential to common mode reponses (DIFF TO COM NEXT) assume a common mode impedance of 75 ohms, a value whose absolute value need not be exact for this purpose. Due to the symmetry of the contact wire arrangement, differential to differential NEXT responses (DIFF to DIFF NEXT) of pair 1 to side pair 4 or pair 3 to side pair 4 is identical in magnitude and polarity to pair 1 to side pair 2 and pair 3 to side pair 2, respectively. However DIFF to COM NEXT responses for pair 1 to 4 (or 4 to 1) and pair 3 to pair 4 (or 4 to 3) have the same magnitude, but of opposite polarity of pair 1 to 2 (or 2 to 1) and pair 3 to pair 2 (or 2 to 3), respectively.
The polarity of the crosstalk generated by the inline structure of FIG. 2A is the same as that generated by the front end of a typical communication plug due to its inline wiring layout and configuration of the plug blades; hence, the large negative pair 1 to pair 3 (1–3) differential to differential NEXT (inductive plus capacitive) is non-compensating and counterproductive. Similar conclusions apply to the other pair combinations. Because the 1–3 pair combination generates a large differential to differential NEXT, compensation for the 1–3 pair can be difficult, but can be partially generated in the remaining parts of the lead frame. Balance of the 1–3 pair combination is not an issue as indicated by the 0 values for differential to common mode NEXT conversion. However, the differential to common mode pair 3 to 2 and pair 2 to 3 NEXT levels are comparatively large, indicating a large unbalance for these pair combinations. The pair 1 to 2 and pair 2 to 1 values also indicate unbalance, but to a lesser extent. It is primarily the large pair 3 to 2 and pair 2 to 3 unbalance, as well as the corresponding pair 3 to 4 and pair 4 to 3 unbalance, that can contribute to poor channel alien NEXT performance. A better balanced lead frame, particulary for the pair 3 to pairs 2 and 4 differential to common mode conversions, would be desirable.
In some prior jacks, the individual contact wires of the jack are made to separate from each other on the lead frame as they approach the PWB into which they mount and terminate. The resulting stagger pattern is seen in U.S. Pat. No. 6,086,428 to Pharney et al. The cross-section of this region of contact wires of such a jack is shown in FIG. 2B, and, for a final stagger height of 0.1 inch, the per unit length NEXT values are shown in Table 2. This would be the case for the lead frame of FIG. 2 without the “jog” created by the laterally traversing section present in the contact wires of pair 1.
TABLE 2NEAR END CROSSTALK RESULTS - STAGGER PATTERNPair A to BPair A to BPair B to ADIFF TO DIFF NEXTDIFF TO COM NEXTDIFF TO COM NEXTPair A to BXLXCTOTALXLXCTOTALXLXCTOTAL1 to 315.021.4516.472.880.423.30−2.88−0.42−3.303 to 29.780.9510.7311.031.6112.64−0.2650.3870.1201 to 210.021.1111.13−5.38−0.88−6.26−5.38−0.88−6.26units for all values in mV/V/in.Notably, the per unit length coupling polarity has flipped relative to the in-line configuration for the differential to differential NEXT of the 1–3 and 2–3 pair combinations, so these pair combinations now yield compensating coupling. (Again, differential to differential NEXT for the 3–4 pair combination is the same as the 2–3 pair combination). Dimensionally, the longer the lead frame is after the polarity has flipped and before attachment to the PWB, the more cross talk compensation is introduced. It has been the 1–3 and 2–3 differential to differential compensation aspects that have rendered the stagger pattern advantageous (even though the 1–2 differential to differential NEXT is counterproductive, the levels are such that normal compensating procedures on the PWB have been sufficient). But with higher performance standards, balance is now a significant variable, and the large counterproductive differential to common mode pair 3 to pair 2 (and pair 3 to pair 4) mode conversion of the stagger pattern is highly undesirable.
The prior jack lead frame embodiment shown in FIG. 2 employs a contact wire configuration that not only staggers, but also has leads that include laterally traversing sections (termed herein “traverses”) that vary the coupling of the contact wires of the jack. For example, after the leads stagger apart, the leads of pair 1 “jog” laterally to closely couple the “tips” of pairs 1 and 3 and the “rings” of pairs 1 and 3. FIG. 2C shows the resulting final cross section, and Table 3 shows the cross talk levels reached, after pair 1 traverses closer to pair 3 and a separation height of 0.1 inch has been reached. (This height is choosen for direct comparison to results given in Table 2 above had a conventional stagger pattern been maintained.)
TABLE 3NEAR END CROSSTALK RESULTS - STAGGER AND TRAVERSEPair A to BPair A to BPair B to ADIFF TO DIFF NEXTDIFF TO COM NEXTDIFF TO COM NEXTPair A to BXLXCTOTALXLXCTOTALXLXCTOTAL1 to 336.283.4939.770000003 to 29.780.9510.7311.031.6112.64−0.2650.145−0.1301 to 28.010.898.92.990.383.37−2.99−0.38−3.37units for all values in mV/V/in.Although differential to differential compensation levels are about the same as the staggered pattern of FIG. 2B for pairs 3 to 2 and pairs 1 to 2, the pair 1 to pair 3 differential to differential compensation efficiency increased dramatically (39.77 mV/V/in from 16.5 mV/V/in) with the addition of the lateral traverses in pair 1. The efficient 1–3 differential to differential compensating ability of this lead frame can be very desirable. The pair 1 to 2 differential to differential NEXT is counterproductive (as would be pair 1 to 4), albeit manageable for some levels of jack performance but it has been found to be manageable. However, even with this jack's improved 1–3 differential to differential compensating ability, Table 3 demonstrates that the jack still has serious differential to common mode NEXT conversion problems for the pairs 3 to 2 (and pairs 3 to 4) combinations. The same mode conversion levels are generated that the stagger pattern alone revealed (12.64 mV/V/in). This means that the pair 3 to 2 mode conversion of the very unbalanced inline section (i.e., the free end segments of the contact wires) would be added to the counterproductive levels generated in transition regions (where some in-line geometry is followed by staggering), and subsequent regions after pair 1 traverses. A similar issue arises with jacks incorporating the simple staggered leadframe of FIG. 2B. Hence, these prior lead frames only partially reduce the mode unbalance of the pair 3 to 2 and pair 3 to 4 differential to common mode NEXT relative to maintaining the in-line geometry over the same length. Although the pair 1 to 2 and 2 to 1 differential to differential and differential to common mode levels are reduced with the cantilever from the rear lead frame of FIG. 2C, the large 3 to 2 unbalance can still be problematic.
U.S. Pat. No. 6,443,777 to McCurdy, supra, discloses a prior art jack in which the fixed end segments of pair 3 include traverses that cause portions of the fixed end segments of the contact wires of pairs 1 and 3 to form a rectangle (see FIG. 2D).